This invention relates to cycloconverter devices, and more particularly to cycloconverter devices used in combination with rotary electrical machines (e.g., motors and generators). The electrical machine cycloconverters of the present invention include a series of semiconductor switches connected to an array of armature coil taps that are used to dynamically control the number of generator armature coils connected to an external AC load, or the number of motor armature coils connected to an external source of power.
Conventional electrical machine cycloconverters have several sources of loss. For example, these devices often exhibit significant armature, semiconductor switch and electrical filtering losses. Excessive armature resistive losses often are produced because load current must flow through all of the armature coils during active operation. Moreover, unnecessary switching losses typically are incurred in conventional cycloconverters because conventional electrical machines cannot precisely regulate their internally generated voltage (beyond simple field control). In addition, the output waveform of conventional electrical machine cycloconverters typically exhibits a high degree of harmonic distortion and thus often require an elaborate electrical filter network. Such filter networks often are expensive, bulky and cause an overall loss of efficiency of the entire system.
One application for known electrical machines is as a component in a continuous power system. Such systems often include a prime mover that is driven by either an AC signal or fuel, a generator coupled to the prime mover that produces power upon rotation by the prime mover, and conversion circuitry that converts the generator output power to useful AC power. For example, Farkas, U.S. Pat. No. 4,827,152 describes an uninterruptible power supply system in which short-term transient power is produced by a flywheel and hydraulically driven motor coupled to an alternator/generator, while long-term transient power is supplied by a diesel engine. As described above, however, variations in the output power of the flywheel/hydraulic supply are inevitable as the device's rotational speed slows down prior to the diesel engine coming on-line. Moreover, such systems are often complicated and expensive due to the fact that they must be designed to handle maximum load conditions, even though such conditions rarely occur (for example, Farkas includes a hydraulic drive for "redundancy for large amperage critical applications").
In view of the foregoing, it is an object of this invention to provide improved electrical machine cycloconverters that efficiently convert a variable speed mechanical input into a highly controllable AC output.
It also is an object of this invention to provide improved electrical machine cycloconverters that efficiently convert an AC electrical input into a highly controllable variable speed mechanical output.
It further is an object of the present invention to provide methods and apparatus for reducing switching losses of electrical machine cycloconverters.
A still further object of this invention is to provide methods and apparatus for reducing armature resistive heating losses of electrical machine cycloconverters.
Another object of this invention is to reduce the electrical filter requirements of electrical machine cycloconverters.
It is an additional object of the present invention to provide methods and apparatus for providing continuous power systems that include isolated motor and generator functions that efficiently produce output power while preventing intermittent utility outages from affecting the load.